Shoppers heading online to purchase holiday gifts will find they're being charged sales tax at some websites where they weren't before. The reason: the Supreme Court.

A June ruling gave states the go-ahead to require more companies to collect sales tax on online purchases. Now, more than two dozen have moved to take advantage of the ruling, many ahead of the busy holiday shopping season.

"Will your shopping bill look any different? ... The answer right now is it depends," said Jason Brewer, a spokesman for the Retail Industry Leaders Association, which represents more than 70 major retailers.

Whether shoppers get charged sales tax on their online purchases comes down to where they live and where they're shopping.

Before the Supreme Court's recent decision , the rule was that businesses selling online had to collect sales tax only in states where they had stores, warehouses or another physical presence. That meant that major retailers such as Apple, Best Buy, Macy's and Target, which have brick-and-mortar stores nationwide, were generally collecting sales tax from online customers. But that wasn't the case for businesses with a big online presence but few physical locations.

Now, states can force out-of-state sellers to collect sales tax if they're doing a fair amount of business in the state. That means retailers such as Overstock.com, home goods company Wayfair and electronics retailer Newegg can be required to collect tax in more states. Those companies were involved in the case before the Supreme Court, but a wide range of businesses from jewelry website Blue Nile to clothing and outdoor company L.L. Bean and electronics retailer B&H Photo-Video are also affected.

Before the Supreme Court's decision, Overstock was collecting sales tax in eight states. Now, it's collecting sales tax nationwide. Jonathan Johnson, a member of Overstock's board of directors, said a small number of customers reached out to ask about the change when it happened but the company now hasn't had a question about it in months. Wayfair, for its part, was collecting sales tax in 25 states before the decision. Now it's collecting sales tax in 36 of the 45 states with a sales tax.